Re: [netmod] WG adoption poll draft-bjorklund-netmod-rfc7227bis-00

Robert Wilton <> Tue, 19 September 2017 13:49 UTC

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Date: Tue, 19 Sep 2017 14:49:09 +0100
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Subject: Re: [netmod] WG adoption poll draft-bjorklund-netmod-rfc7227bis-00
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Hi Lada,

On 19/09/2017 14:37, Ladislav Lhotka wrote:
> Martin Bjorklund <> writes:
>> Ladislav Lhotka <> wrote:
>>> Hi,
>>> I support the adoption but I propose two conceptual changes:
>>> 1. Introduce a new module name and namespace so that it is not
>>> necessary to carry along the deprecated baggage. If readability is
>>> the primary concern, this is IMO the way to go. Instead of
>>> "ietf-ip-2", I'd suggest something like "ietf- ip-nmda".
>>> 2. Avoid obsoleting RFC 7277. I believe the old modules may continue
>>> to be used
>>> in areas where NMDA is an overkill, such as open source home
>>> routers.
>> Why wouldn't NMDA be appropriate in an open source home router?  Note
>> that the new model really just have a single tree instead of two
>> trees, so the data that needs to be instrumented is more or less the
>> same.
> It is quite likely that some parts of the data models will be
> implemented only as configuration but not state data. In the "old style"
> modules it is easy to add a deviation for the node(s) under -state but
> in NMDA style this is not possible because we only have one node.
The new YANG library allows different sets of modules to be available 
for <conventional> datastores vs <operational>.   The operational 
datastore can also have different features supported and different 
deviations vs the conventional datastores.

So, the device can make the same deviations to remove the state leaves 
from <operational>.  Or if they don't want to support the module in 
operational at all then a device could just list it as being supported 
in the conventional datastores and not <operational>.

> There are subtle differences in the schemas for configuration and state
> data that the NMDA concept doesn't address. If you want another example,
> ietf-routing-2 has the "router-id" leaf that is conditional via the
> "router-id" feature. If this feature is not supported, router-id cannot
> be explicitly configured (it is assigned by the system) but in state data
> "router-id" needs IMO be present in any case. But the if-feature
> isn't able to differentiate between configuration and state data if
> there is only one node for both.
The new YANG library also supports this:

The "router-id" feature would be disabled for the conventional 
datastores, but enabled for <operational>.

>> In fact, if we claim that the new architecture is not appropriate for
>> some devices I think we have failed, especially if the conclusion is
>> that we need to maintain two versions of all modules going forward.
> I am not asking for this but, on the other hand, if NMDA versions used a new
> module name and namespace (my item #1, which is what ietf-routing-2
> does), then I don't see any pressing need for obsoleting the old style
> modules.
I think that creating a "-2" versions of these models at this time might 
be a mistake.  I actually think that the "deprecate state leaves" -> 
"obsolete state leaves" -> "delete state leaves" path is a better choice.


> Lada
>> /martin
>>> NMDA
>>> implementors should be aware of the new modules but there is no need to
>>> eradicate the old data models.
>>> #2 applies also to other modules for which the NMDA version is underway.
>>> Lada
>>> PS. The subject is wrong, it shoud be -rfc7277bis-
>>> Lou Berger píše v Po 18. 09. 2017 v 10:33 -0400:
>>>> All,
>>>> This is start of a two week poll on making
>>>> draft-bjorklund-netmod-rfc7227bis-00 a working group document. Please
>>>> send email to the list indicating "yes/support" or "no/do not support".
>>>> If indicating no, please state your reservations with the document.  If
>>>> yes, please also feel free to provide comments you'd like to see
>>>> addressed once the document is a WG document.
>>>> The poll ends Oct 2.
>>>> Thanks,
>>>> Lou (and Kent)
>>>> _______________________________________________
>>>> netmod mailing list
>>> -- 
>>> Ladislav Lhotka
>>> Head, CZ.NIC Labs
>>> PGP Key ID: 0xB8F92B08A9F76C67
>>> _______________________________________________
>>> netmod mailing list